Polyesterurethane elastomers having improved color characteristics



United States Patent This invention relates to a method for improvingthe color characteristics of polyesterurethane elastomers and to themodified polymers produced thereby.. More particularly, thisinvention-.concerns'a method for improving the initial color ofpolyesterurethane elastomers and for enhancing their color-stability inthe presence of light,

which method comprises reacting the polyesterurethan forming ingredientswhile in contact with a critically small amount of an amine-acetic acidchelating agent.

Polyestenlrethane elastomers, also nominally referred to in theliterature as polyesterurethane gums or rubbers,"

elastomeric urethane reaction products'and the like, are made bycondensing low molecular weight polyesters with aromatic diisocyanatesto give high molecular weight linear polymers. The polyesterurethanecanbe the substantially non-crosslinked variety wherein the polymerchain has been extend by the inclusion of'an aliphatic glycol in thepolymerization reactants; or thepolyesterurethane can be of thecrosslinked variety obtained by heating and reacting thelinear'polyesterurethane with additional diisocyanate. Thepolyesterurethane-forming reaction generally is carried out at'elevatedtemperatures,: e.g., Within the range of about 120". C. to 250 C., for

a period of time suflicient to provideisubstantiallycom plete reactionof active hydrogen containing reactants with the available isocyanategroups.

Heretofore, the color of polyesterurethane elastomers" have been darkerthan desired, frequently being a dark yellow and sometimes appearingbrown. This is disadvantageous because it is difiicult to prepare pureWhite elastomers when compounding the rubbers with white pigments, suchas titanium dioxide, if the rubber has a pronounced yellow or browntinge. duce variously colored elastomers having standardized orconsistent color depth if the rubber stock to be com pounded with apigment or dye is essentially colorless or only slightly yellow. Anotherdisadvantage attaching to polyesterurethane elastomers is their tendencyto progressively darken upon prolonged exposure to light. It is,therefore, the object of the present invention to provide a process forproducing lighter-colored polyester, It is a further object toprovideurethane elastomers. modified polyesterurethane elastomers whichhave improved color stability in the presence of ultra-violet:radi-'ation.

It has now been discovered process for producing a polyesterurethaneelastomer by heating and polymerizing a reaction mixture comprising asessential polyesterurethane-forming ingredients: (A) one mol equivalentof a hydroxyl terminated polyester of a saturated, aliphatic glycolhaving from 2 to 10 carbon atoms and having hydroxyl groups on itsterminal carbon atoms and an aliphatic di'carboxylic acid having from 2to 10 carbon atoms and (B) at least 0.7 mol equivalent of an aromaticdiisocyanate;'the color .of said elastomeric reaction product isimproved by incorporating into said reaction mixture, prior to theheating thereof, from 0.03 to 0.4%, based on the weight of the reactionproduct, of a chelating agent which is an acetic acid-substitutedaliphatic alkylene amine having from 1 to 5 acetic acid constituents, 0tov 3 hydroxyl groups attached to terminal carbon atoms of an alkylenegroup, active hydrogen atoms only in said acetic acid groups It is alsoeasier to pro that in the conventional whose valences 'are connectedonly to carbon atoms (i.e.-

1 persed throughout.

most desirable.

"ice

and hydroxyl groups, and 1 to 3 amino nitrogen atoms the amine istertiary amine).

In general, the polyesterurethane products of this in vention areconveniently prepared by first mixing said small amount of chelatingagent, one mol equivalent of polyester, optional polyurethane modifyingcompounds and at least about 0.7 mol equivalent of aromatic diisocyanatetogether at an elevated temperature so that thepolyesterurethane-producing ingredients form a homogeneous'meltcontaining the chelating agent uniformly dis- Normally, a temperature ofabout to C. is sufiicient to obtain this state. The chelating agent is asolid-material which is not soluble in the polyester and/0r diisocyanatein this temperature range. It is therefore advantageously employed inthe form of a fine powder or granulation to achieve a substantiallyuniform dispersion thereofinthe reaction mixture, for example, particleshaving diameters of from about 0.03 mm. to around 2,mm., however,particles smaller than 0.5 mm. are'vpreferred, V

The polymerization ofv the reactants, which is advantageouslyexothermic, is then carried out at a temperature Within the range offrom about C. to about 250 C. At .these elevated'ternperat'ures thechelating agent becomes compatible withthe reactants and appears todissolve therein. .Thereacti'on period ranges from about 3 minutes toabout one hour, the rate of reaction being dependent .on the temperatureemployed. The reaction period needs beno gre'aterthan that required toinsure essentially complete ,stoichiometric utilization of the re-1actants in accordance with their molar equivalencies .as

charged. The reaction should. be carried outunder essentiallyanhydrousconditions with dry reactants, that is, the reaction mixture issubstantially free of Water which would react with 'isocyanate, groupsto formundesirable by-productsi As a practicalmatter, there should beless than about 0.1% and preferably less'than 0.05% of water present inthe reaction mixture. Essentially anhydrous conditions can beassured bysimply heating the polyester and optional modifying compounds at lowpressure before they are mixed with the diisocyanate. j I

The basic polyester reactant embodied in the polyesterurethane isessentially linear and is hydroxyl terminated. It isthecondensationjproduct obtained by an esterification of an aliphaticdicarboxylic acid or an anhydride thereof with a straight chain glycolcontaining 2 to 10 carbon atoms and having itshydr'oxyl groups on theterthe flike,io rl their anhydrides. The dicarboxylic acid may berepresented by the formula HOOC-(C HQ COOH,

where n is 'a number from 0 to 8, preferably 4 to6. In

the esterificatior reactions, molar ratios of more than one mol ofglycol per met r acid are preferred so as to ob tain' essentially linearchains containing a preponderance of terminal. hydroxyl groups.

polyester suitablefor urethaneelastomers is characterized by having anaverage molecular weight between about 400"'and about 5,000, a hydroxylnumber between about 275 and 15 and an acid number of less than I0,preferably less than 7., The quality of the polyurethane productincreases as the acid number of the polyester decreases. An' acid numberof less than about 4.0 is thus more preferred, and an acid number ofless than 2.0 is

The methods and details of manufacturing such polyesters are well known.The

The aromatic diisocyanate embodied in the elastomer of this inventionincludes such compounds as the diphenyl diisocyanates and the diphenylmethane diisocyanates, especially 4,4'-diphenyl diisocyanate and4,4-diphenylene methane diisocyanate; the dimethyl diphenyl methane 5diisocyanates, the diphenyl ether diisocyanates, the dichloro-diphenylmethane diisocyanates, bibenzyl diisocyanate, bitolylene diisocyanate,dianisidine diisocyanate, para-phenylene diisocyanate, meta-phenylenediisocyanate, naphthalene-1,5-diisocyanate, meta-toluene diisocyanate,tetrachloro rn-phenylene diisocyanate, durene diisocyanate, and the likeand mixtures thereof.

The aforementioned optional modifying compound which may be included inthe polyurethane-producing reaction mixture is one that contains anactive hydrogen, i.e., a hydrogen which will react with an isocyanate(NCO) group. In the case of the so-called casting typepolyesterurethanes wherein the ratio of isocyanate groups to all activehydrogen groups in the polymer is greater than 1.0, the optionalmodifying compound therein may be a glycol, diamine or amino alcoholwhich provides additional substituted urea or urethane groups as pointsfor the future crosslinking. The final curing takes place by reactingthe excess isocyanate groups with the substituted urea or urethanegroups at around 100 to 150 C. The casting type polyesterurethanes mustbe processed shortly after mixing the components. In the case of theso-called storage-stable polyesterurethanes which are prepared initiallywith only part of the total diisocyanate to be finally reacted, i.e.,the ratio of isocyanate groups to all active hydrogen groups in theinitial polymerization reaction mixture is less than 1.0, the curing orcrosslinking of the elastomer is accomplished by adding more isocyanatethereto and heating under pressure. Thus, in this polyester-diisocyanatereaction, no modifying compound is required. In the case of thenon-crosslinked, thermoplastic type of polyesterurethane elastomerswherein the number of isocyanate groups in the reaction mixture isessentially equivalent to the number of active hydrogens, the optionalmodifying agent is a dihydroxy compound. 1

Examples of the preferred type of polyesterurethane elastomersusceptible to color improvement and stabili- Zation in accordance withthe practice of this invention are described in US. Patent No. 2,871,218and copending US. application Serial No. 294,933 of Robert M. Garvey andEdmond G. Kolycheck, filed July 15, 1963. Each reference describes apolyesterurethane elastomer which is substantially free of crosslinkedstructures and substantially soluble in such solvents as cyclohexanone,tetramethyl urea and dimethyl formamide. Said elastomer comprises thereaction product obtained by heating a mixture comprising as essentialingredients: (A) 1.0 mol of an essentially linear, hydroxyl terminatedpolyester of a saturated aliphatic glycol having from 2 to 10 carbonatoms and the hydroxyl groups on the terminal carbon atoms and analiphatic dicarboxylic acid containing from 2 to 10 carbon atoms, or theanhydride of the dicarboxylic acid, ,said polyester having a molecularweight between 600 and 1,200' and an acid number less than 10, (B) fromabout 1.1 to 3.1 mols of a diphenyl diisocyanate having an isocyanategroup on each phenyl nucleus, and (C) from about 0.1 to 2.1 mols of asaturated, aliphatic, free glycol containing from 2 to 10 carbon. atomsand having hydroxyl groups on its terminal carbon atoms, the molaramount of the polyester and the free glycol combined being essentiallyequivalent to the molar amount of the diphenyl diisocyanate so thatthere are essentially no unreacted isocyanate or hydroxyl groups in thepolyesterurethane product. The glycol serves as a chain extendingconstituent in the polymeric structure of the urethane elastomer. Theabove-described polyesterurethane, marketed under the trade name Estaneis a thermoplastic, extrudable, moldable, abrasion resistant, toughelastomer.

Another example of the substantially non-crosslinked type ofpolyesterurethane is that described in US. Patent No. 3,001,971 as beinga weather resistant elastomer comprising the reaction product of one molof polyester, from about 1.0 to 5.0 mols of an aromatic dihydroxylcompound and from about 2.0 to 6.0 mols of an aromatic diisocyanate, themolar amount of the diisocyanate being substantially equivalent to themolar amount of the polyester and the aromatic dihydroxyl compoundcombined.

An important shelf-stable polyesterurethane, exemplary of thosesusceptible to color improvement when modified according to thisinvention is described in US.

' Patent No. 2,625,535, wherein the polyester component is reacted witha molar deficiency of aromatic diisocyanate to provide an elastomerwhich is curable at a later time by causing it to react with additionaldiisocyanate. A further example of the type of product which may bemodified in accordance with this invention is disclosed in U.S. PatentNo. 2,770,612, which describes an easily processable polyesterurethanerubber obtained by reacting one mole of a polyester of ethylene glycoland an aliphatic dicarboxylic acid with from 1.02 to 1.1 mols of anaromatic diisocyanate. The non-crosslinked product may be cured bysubsequent reaction with additional diisocyanate. Of course, theabove-described polyesterurethane elastomers are merely exemplary sincethere are many types and variations known to the trade.

As stated previously, the chelat-ing agent, which is incorporated intothe p-o lyesterurethane-forming reaction mixture prior to the initiationof polymerization by the application of heat thereto, is an aceticacid-substituted aliphatic alkylene amine having from 1 to 5 acetic acidconstituents, from 0 to 3 hydroxyl groups attached to terminal carbonatoms of an alkylene group, active hydrogen atoms only in said aceticacid constituents and hydroxyl groups, and 1 to 3 nitrogen atoms bondedonly to carbon atoms. Chelating agents conforming to these requirementsinclude the alkylene diamine tetraacetic acids represented 'by theformula:

(CH2OOOH):

where y is an integer of 2 to 8. The commercially availableethylenediaminetetraacetic acid (y is 2) gives excellent results. Of asimilar nature are the triamine pentaacetic acids represented by theformula:

where y is an integer of 2 to 8. Diethylenetriaminepentaacetic (y is 2)is preferred.

Exemplary of hydroxyl-containing chelating agents operable herein arethe N ,N-di(hydroxya lkyl)substituted glycines represented by theformula:

CHzOOOH where y and z are each integers of from 2 to 8. Preferred ishydroxyethyl-ethylenediaminetriacetic acid (y is 2 and z is 2).

where R is' a hydrocarbon group having from 6 to 22 carbon atoms, and Ris an ralkylene group having from 2 to carbon atoms. It is preferredthat R be an alkyl group and R have from 2 to 3 carbon atoms.Illustrative specific compounds falling into this class are thefollowing:

The chelating agents of this class are readily prepared by reactingchloroacet-ic acid in neutral solution with various alkyl-substitutedalkylene polyamines.- The acid reacts.

with the active hydrogen on the amino nitrogens to yield triaceticacidsubstituted polyamine and byproduct HClI The acid chelator isprecipitated by lowering the reaction pH to an acid level of 2. Theproducts are solids and easily recovered by filtration, then washed anddried. The preparation of these triacetic acid-substituted alkylenediamine chelating agents is more fully described in the copending patentapplication of R. E. Morris, R. D. Taylor and R. J. Fa'wcett Serial No.192,080, filed May 3, 1962, now U.S. Patent 3,228,904. The incorporationof such chelators into polyesterurethane elastomers of the linear,uncrosslinked type described in the aforementioned U.S. Patent 2,871,218is disclosed in the copending patent application of C. S. Schollenbergerand W. T. Murphy, Serial No. 301,174, filed August 9, 1963, wherein theamount of chelator added to the elastomers is from 0.5 part to 5.0 partsper 100 parts by weight of the clastomer. When added to the solidelastomer or to a solution of the elastomer in the manner and amount setforth in said copending application, the chelator additive serves toinhibit environmental'stress cracking in the elastomer, but the colorcharacteristics of the product are not affected. The method and resultsthereof are thus distinguished from the procedure embodied in thisinvention wherein 0.03 to 0.4% of the chelator is initialy added to thecompounds which are subsequently reacted to form the polyesterurethane;the additive in such a critically small proportion serves as a colormodifier and not as an inhibitor for stress cracking.

The mechanism or manner in which the small amount of chelating agentadded to the polyesterurethane forming reactants improves the colorcharacteristics of the polymers subsequently produced therefrom is notknown.

Significantly, it has been found that the admixture of a chelating agentembodied herein into a mixture of compounds subsequently reacted toproduce a polyetherurethane elastomer (i.e., where the polyester, of theaforesaid polyesterurethane formulations is replaced by a polyalkyleneether glycol) does not result in a color improvement of thepolyetherurethane rubber. However, it should be noted that in theproduction of the so-called polyetherestenlrethanes which are made bymixing together various polyesters and polyethers, or various glycols,polyalkylene ether glycols and dibasic acids, and then reacting themwith aromatic diisocyanates in varyng amounts, the chelatiug agent willhave a beneficial effect on color, provided there is a substantialamount of polyester present.

As aforementioned, the chelating agent is added to thepolyesterureth-ane-forming mixture in a critically small amount,specifically 0.03 to 0.4% by weight of the reactants polymerized, andsince the reaction is substantially complete, the amount of chelator cancorrespondingly be expressed as 0.03 to 0.4% of the polyesterurethaneproduct. No significant improvement in the color characteristics of thepolymer is observed if less than about 0.03% of chelator is used. Whengreater than about 0.4% is charged, the product elastomer has inferiormechanical properties, and in particular, a pronounced decrease intensile strength is observed. Moreover, although the color of theelastomer becomes progressively better as the amount of chelator isincreased within said range of 0.03% to about 0.4%, a further increaseis not beneficial to color and is quite harmful with regard to otherphysical properties. The preferred amount of chelating agent from thestandpoint of attaining a pronounced color improvement without asignificant reduction in tensile strength lies in the range of about0.05 to 0.2%.

Representative methods of synthesizing some of the preferred ohelatingagents embodied herein are next presented. Dodecyliminodiacetic acid isprepared as follows: Chloracetic acid (1.1 mole) in 800 ml. of ethanolis neutralized by the adtition of 125 ml. of 10 normal aqueous sodiumhydroxide. Dodecylamine (0.5 mole) is added to the mixture and thesolution is heated to C. The pH is maintained at from 8 to 10 by thegradual addition of more sodium hydroxide solution until thetheoretically required amount of sodium hydroxide has been added. Thereaction mixture is then brought to room temperature and thedodecyliminodiaoetic acid is precipitated by bringing the pH of themixture to 2. with concentrated hydrochloric acid. The product isisolated by filtration and is washed twice with distilled water anddried to a constant Weight of 141.3 g. (94% of theory).

In a similar manner octadecyliminodiacetic acid and otheralkyliminodiacetic acids are prepared.

A chelating agent having the structure where Ris a mixture of alkylgroups having an average of 13 carbon atoms is prepared as follows.Chloracetic acid (2.24 moles) in 400 ml. of methanol is neutralized with31% NaOH solution. 0.25 mol of Duomeen CD (RNHCH CH CH NH wherein R is amixture of alkyl groups having an average of 13 carbon atoms) is addedthereto. The reaction mixture is brought to 7073 C. and its pH ismaintained at 8-10 by the addition of more NaOH solution until the pHbecomes fairly constant for a period of time. The mixture is cooled andthe product is precipitated with hydrochloric acid (pH of 2). The solidis isolated by filtration, washed and dried. In a similar mannerchelating'agents of the: formula wherein R is a mixture of alkyl groupshaving an average of from 17 to 18 carbon atoms, are prepared startingwith Duomeen S and Duomeen T mixed alkyl-substituted alkylene diamines.The Duomeens are sold by the ents reacted to form the polyesterurethaneelastomer, which weight is essentially equivalent to the total weight ofthe product elastomer. The data relating to the physical properties ofthe elastomers were obtained ac- Armour Industrial Chemical Company,Chicago, Illinois. cording to the tests and procedures listed below. TheEXAMPLES OF POLYESTERURETHANE slyrtrbglli lgatig [in vaatsabllgtofn(212g: indicates that the particular PREPAMTION Ultimate tensilestrength in lbs./ sq. inch, percent ulti- The polyesterurethaneelastomers described in the folmate elongation (i.e. at break) andmodulus (tensile lowing examples were prepared as follows. One mol ofstress) at 300% elongation were determined as per ASTM 1,4-butanediolwas mixed and stirred for about one to test method D412-51-T. fiveminutes at a temperature of about 85 to 100 C. Hardness was determinedusing a durometer as per with one mol of a hydroxyl terminatedpolyester[hydroxyl ASTM test method D67659T. poly(tetramethyleneadipate)] having a molecular weight The color of an elastomer wasmeasured by comparof 1,000, an acid number of 3.0 and a hydroxyl numbering the color of a 2% solution of the polyesterurethane of 106. Themixture was separated into two or more in tetrahydrofuran with thewell-known APHA color measured portions. Chelating agent was added toone standards. Unless otherwise indicated, the colors reor more of theportions, while no chelating agent was ported are initial colors, thatis, the color of the product added to at lea t o f th rtion measuredimmediately after it had been molded into a To the individual portionsof the diol-polyester mixsheet. ture were charged essentiallystoichiometric equivalent Example I amounts of diphenylmethane-p,p-diisocyanate (usually referred to as MDI), that is, themolar amount of the This series of experiments compared theeffectiveness diisocyanate was substantially equal to the molar amountof three chelating agents in inhibiting color formation in of thepolyester and glycol combined. The reaction mixthe polyesterurethanesynthesis. The chelator concenture was stirred for 3 to 8 minutes at 140C. and aged tration was 0.17% in experiments 2-4.

Elastomer Experiment Chelating Agent APHA Color 1(C0ntr0l)- None 2Etliylenedlamlnetetraacetlc acid 35 CHIC/00H 3 (Cisav)uvs.-N(CH:)a-N-(CHzCOOH): 35

4 Dodecyllmlnodiacetlc acid 30 at 140 C. for about 30 minutes on theaverage. The Example II polyesterurethane product was cooled to yield aflexible elastomer which was subsequently molded at 175 C. for In thigrou f experiments th ff t f h h l ti five minutes at 20,000 to 35,000P- -g into Sheets 7 agent on the mechanical physical properties of theelasinch thick to provide samples for physical testing. The elastomerslacking the chelating agent were designated as control samples. Theconcentration of ehelating agent is reported in the tables of data aspercent by Weight tomer, as well as on its color, were noted. The datais tabulated in Table A. It is seen that use of the chelat-or additivesresults in the sacrifice of some tensile strength but the hardness ofthe elastomer is not appreciably based on the combined weight of thesubstituent ingredi- 5 affected.

TABLE A Physical Properties of Polycstenlrcthane Experiment ChelatingAgent, (Amount) API-IA Shore Color Tensile Elong. Modulus Hardness,

A Scale 5 (Control) None 20 9, 675 570 1, 500 88 6Ethylenediaminetetraacetic acid, (0.17%) 10 6, 300 540 1, 500 36 7(Control) N one 8, 100 530 1, 380 87 C H 0 O O H 8((1131137),ve.N-(CH:)a-N(CH2C 0 0H) 2, (034%) 30 7, 350 570 1, 230 87 9(Control) None 50 8,400 510 1, 500 86 10 Dodecyliminodiacetic acid,(0.34%) 15 6, 960 600 1, 390 None 45 7, 500 600 1, 200 89 N,N-dihydroxyethyl glycine, (0.17%) 15 5, 010 660 1, 080 85 The resultsof this series of experiments-viewed with the results of othersdescribed herein illustrate that (a) at least about 0.03% of chelator isrequired to provide 10 thesized withandwithout'chelator, Thepolyesterurethane samples were exposed to ,ultravioletradiation from aGeneral Electric Company germicidal lampfor up to 14 days. The colors ofthe polymers. were measured by a a color improvement f thepolyestemrethane and 1, Photovolt (Photoelectric) Reflection Meter.model 610, relatively large amounts of chelator have a significant a P0f the PhO'IOVOIt COTPOIatIOII, New York, degradative effect on thephysical properties of the poly- Employing this measuring device, theinstrument readings esterurethane with little or no improvements incolor become W61iI1 Value as the 0 of a P y Specimen characteristics.The data are presented in Table B. darkens. The data presented belowshowthat the chela- TABLE B Physical Properties of Polyesterurethane'Experiment Chelating Agent, (Amount) APHA Shore Color Tensile Elong.Modulus Hardness, A Scale 13 (Control) Nnn 25 3, 790 550 1, 380 87(llHsC O OH 14 (019E517) nvs.N(CH2)aN-(CH2O O OHM, (ll-07%)-; 15 7, 830560 1, 425 87 CHaC O OH (0185) ave." N(CH2)3N(CH2C O OH, (0.16%) 8, 240570 1, 320 87 None 40 6, 880 590 1, 200 87 Dodecyliminodiaeetic acid,(0.007%) 40 7, 460 590 1, 150 85 Dodecyliminodiacetic acid, (0.007%) 206,880 600 1, 180 86 Dodeeyliminodjacetic acid, (0.7%) 20 2, 240 710 80086 None 45 7, 440 570 1, 290 85 Dodecyliminodiacetic acid, (0.034%) 7,890 580 1,290 85 Dodecyliminodiacetic acid, (0.05%) -M 35 7,860 5701,290 87 V Dodecyliminodiacetic acid, (0.17%) 30 7,800 600 1,350 88 1Example" I V.

This example-illustrates thatthe use of a chelator in accordanceWith-this invention not only improves the initial color of thepolyesterurethane but also serves to inhibit color formation in thepolyurethane as it ages; in fact, there is a surprising tendency for thecolor of the polyurethane to become less intense as the materialundergoes prolongedexposure to light, i .e., as if light had a bleachingeifect on the'polymer made with chelating agent. In this series ofexperiments, the chelating agent was the triacetaic acid-substitutedalkylene diamine having the structure V g The color of thepolyesterurethane was determined immediately following its manufacture;samples thereof then were exposed to natural light for the indicatedperiods and the colors measured with the following results.

This example shows the eifects of prolonged exposure to ultravioletlight on polyesterurethane elastomers syntor gives improvedinitial'color and :also protects the polymer against U.V. catalyzeddegradation.

This example illustrates the present inventions specific applicabilityto polyesterurethanes. Instead of the polyesterurethane elast omerdescribed in the preceding examples, a polyetherurethane elastomerhaving similar properties was prepared by essentially the sametechniques (i.e., corresponding mor-al ratios and reactiontemperatures); however, the formulation differed from the earlier recipein that a polypropylene glycol having a molecular weight of 1000 wassubstituted for the hydroxyl terminated polyester used previously. Thepolypropylene glycol was blended with the 1,4-butanediol and to thismixture was added 0.01% of stannous octoate catalyst. The blend wassplit into two equal portions, each of which was reacted with equimolarquantities of diphenyl methane-p,p'-diioscyanate, one reaction mixturecontaining in admixture 0.17% of dodecylirninodiacetic acid, the othermixture lacking this additive. Comparison of the colors of thepolyetherurethane products revealed that the one made with the chelatingagent had 'a color with approximately twice the intensity as that of thecontrol sample.

It is to be understood that the foregoing examples of specificembodiments of the invention are merely illustrative and not limitingsince modifications and variations may be made without departing fromthe scope and spirit of the invention as defined by the appended claims.Stated differently, the essence of invention lies in forming apolyesterurethane elastomer by reacting as essential ingredients apolyester and an aromatic diisocyan-ate, in the presence of thedescribed chelating agent. Additional modifying compounds and additivesincorporated in the polymers, either chemically by copolymerization, ormechanically by physical admixture of additives such as antioxidants andstabilizers, are contemplated to be within the ambit of the invention asit is well known to influence the physical characteristics ofpolyurethanes with sundry coreactants and modifiers.

We claim:

1. A polyesterurethane elastomer having improved color comprising thereaction product of a mixture of (A) a hy-droxyl terminated polyester ofa saturated aliphatic glycol containing from 2 to 10 carbon atoms and analiphatic dicarboxylic acid containing from 2 to 10 carbon atoms, saidpolyester having an average molecular weight between about 400 and 5000and (B) from 0.03 to 0.4% based on the weight of the total of (A) and'(C) of an acetic acid substituted aliphatic alkylene amine having from1 to acetic acid constituents, from 0 to 3 hydroxyl groups attached toterminal carbon groups of an alkylene group, active hydrogen atoms onlyin said acetic acid groups and hydroxyl groups and 1 to 3 amine nitrogenatom val-ences are connected only to carbon atoms, with (C) at least 0.7mol equivalent per mol of polyester of an aromatic diisocyanate.

2. The polyesterurethane of claim 1 wherein (A) is a polyester of aglycol having the formula HO(CH OH wherein at is 2 to 6 and adioa-rboxylic acid of the formula H'OOC(CH COOH wherein n is preferably4 to 6 and (B) is an aliphatic alkylene amine selected from the groupconsisting of those having the formula III (CH2)yOH NCH2C O OH IV(CHzCOOI-D2 CI-IzCOOI-I I I(OHz)yN (GHQ-OH where y and z are integers offrom 2 to 8,

V XN(CH2COOH)2 where X is an alkyl group having from 8 to 24 carbonatoms and VI CHzCOOH RNR-N(CH2C o OH)2 where R is a hydrocarbon grouphaving from 6 to 22 carbon atoms and R is an alkylene group having from2 to 10 carbon atoms, present in amount from 0.05 to 0.2%.

3. The polyesterurethane of claim 2 wherein (B) is clodecyliminodiaceticacid.

4. The polyesterurethane of claim 2 wherein (B) is VI and R contains anaverage of 18 carbon atoms.

5. The polycste-rurethane of claim 2 wherein (B) isethylenediaminetetraacetic acid.

6. The lpolyesterurethane of claim 2 wherein (A) is hydroxyl poly(tetramethylene adiphate) (B) is an amine acetic acid having thestructure CH2GOOH RI1\I(CH2) x" N(OH2) C O OH wherein x is 1 to 6 and Ris an :alkyl group having an average of 13-18 carbon atoms and (C) is adiphenyl diisocyanate having an isocyanate group on each phenyl nucleus.

7. The polyesterurethane of claim 2 wherein (A) is hydroxylpoly(tetramethylenc adipate) (B) is an aliphatic al-kylene amine havingthe structure wherein x is 1 to 6 and R is an alkyl group having anaverage of 1318 carbon atoms and (C) is a diphenyl diisocyanate havingan isocyanate group on each phenyl nucleus and there is also present inthe reaction mixture an aliphatic glycol containing 2 to 10 carbon atomsthe molar ratios of (A) and (B) being substantially equivalent to (C).

References Cited by the Examiner UNITED STATES PATENTS 1/1947 Bersworthet al. 260-3l.8 1/ 1966 Morris et a1. 260-45.8

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,298,995 January 17, 1967 Robert R. Bloor et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 26, for "extend" read extended column 5, line 65, for"initialy" read H initially column 6, lines 74 and 75, the formulashould appear as shown below instead of as in the patent:

cn coon R-N-CHZCHZCHZ-N-(CHZCOOH)2 columns 9 and 10, TABLE B secondcolumn, line 8 thereof, for "(0.007%)" read (0.07%) column 10, line 70,for "diioscyanate" read diisocyanate column 12, line 24, for "adiphate"read adipate Signed and sealed this 17th day of October 1967.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

1. A POLYESTERURETHANE ELASTOMER HAVING IMPROVED COLOR COMPRISING THEREACTION PRODUCT OF A MIXTURE OF (A) A HYDROXYL TERMINATED POLYESTER OFA SATURATED ALIPHATIC GLYCOL CONTAINING FROM 2 TO 10 CARBON ATOMS AND ANALIPHATIC DICARBOXYLIC ACID CONTAINING FROM2 TO 10 CARBON ATOMS, SAIDPOLYESTER HAVING AN AVERAGE MOLECULAR WEIGHT BETWEEN ABOUT 400 AND 5000AND (B) FROM 0.03 TO 0.4% BASED ON THE WEIGHT OF THE TOTAL OF (A) AND(C) OF AN ACETIC ACID SUBSTITUTED ALIPHATIC ALKYLENE AMINE HAVING FROM 1TO 5 ACETIC ACID CONSTITUENTS, FROM 0 TO 3 HYDROXYL GROUPS ATTACHED TOTERMINAL CARBON GROUPS OF AN ALKYLENE GROUP, ACTIVE HYDROGEN ATOMS ONLYIN SAID ACETIC ACID GROUPS AND HYDROXYL GROUPS AND 1 TO 3 AMINE NITROGENATOM VALENCES ARE CONNECTED ONLY TO CARBON ATOMS, WITH (C) AT LEAST 0.7MOL EQUIVALENT PER MOL OF POLYESTER OF AN AROMATIC DISSOCYANATE.